Some industrial processes are sensitive to temperature. For example, some plastic manufacturing processes require that a material be kept within a relatively narrow temperature range for a period of time.
Some conventional industrial processes use mechanical means, such as a bimetal thermostat, to regulate temperature. Bimetal thermostats exploit the differential expansion of two metals to actuate a switch. In this way, a cooling or heating system can be activated if the sensed temperature becomes too high or too low. While bimetal thermostats are reliable and offer good enough control for home heating and cooling applications, they do not offer sufficiently precise control for some industrial processes. Further, bimetal thermostats are characterized by significant hysteresis to prevent frequent powering and depowering of, for example, a heater. While this characteristic is desirable in home heating applications, it yields poor control for temperature-sensitive applications, such as industrial processes. Other mechanical means for regulating temperature, such as pneumatic thermostats, also offer imprecise control.
Other conventional industrial processes use programmable logic controllers (PLCs) to regulate temperature. For example, a PLC may be connected to a thermocouple via an analog-to-digital converter (ADC) that converts the analog voltage signal generated by the thermocouple to a digital value that can be used by the PLC to control temperature. PLCs offer more precise control than is possible with a bimetal thermostat. However, they are relatively costly.